AB1294 SAFETY OF COVID-19 VACCINES AND HEALTH CARE UTILIZATION FOLLOWING VACCINATION AMONG ADULTS WITH RHEUMATOID ARTHRITIS – A POPULATION-BASED SELF-CONTROLLED CASE SERIES ANALYSIS
Authors: J. Lee, S. Bernatsky, J. Kwong, Q. Li, T. Kwok, J. Widdifield
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Although adverse events of special interest (AESIs) following COVID-19 vaccination are considered to be rare, emerging reports have suggested that risk of AESIs may be higher in certain subgroups of individuals. The self-controlled case series method represents a useful approach to study adverse events whereby an individual's risk is compared between a control pre-exposure period and a risk period following vaccine exposure. <h3>Objectives</h3> This study assessed whether COVID-19 vaccines were associated with an increase in AESIs and health care utilization [emergency department (ED) visits, hospitalizations, and rheumatologist visits] among adults with rheumatoid arthritis (RA). <h3>Methods</h3> We used the Ontario RA Database, a validated Canadian population-based cohort. Among adults with an RA diagnosis, we identified those who received at least 1 COVID-19 vaccine. AESI included Bell's Palsy, Idiopathic Thrombocytopenia, Acute Disseminated Encephalomyelitis, Myocarditis, Pericarditis, Guillain-Barre syndrome, Transverse Myelitis, Acute Myocardial Infarction, Anaphylaxis, Stroke, Deep Vein Thrombosis, Pulmonary Embolism, Narcolepsy, Appendicitis, and Disseminated Intravascular Coagulation. Secondary outcomes included all-cause ED visits, hospitalizations, and rheumatology visits (a potential proxy for disease flare). The study end date was March 2022. Self-controlled case series analyses were used to determine event rates in any 21-day risk period following vaccination compared to control periods. For rheumatologist visits, the risk window was confined to a 30-day risk period. Control periods were defined as 6 months prior to the first vaccination [with a 14-day washout period before first dose, as patients may wait until they are in relatively good health before receiving a vaccine]; Control periods in between doses start on Day 22 from the last dose and ends 14 days prior to the next dose; and a final control period commencing after the final dose risk period (up to a maximum of 6 months). Relative incidence (RI) rates were estimated (using Poisson Regression) across risk windows relative to control periods. Relative incidence rate ratios (RIR) in each risk period vs control period were estimated using non-RA comparators (matched on sex, age, and region of residence). <h3>Results</h3> In total 123,466 RA patients and 493,864 comparators were included. 71% of individuals were female and the median age of RA patients was 65 years (IQR: 55-74), with a median RA duration of 9.3 years (IQR: 4.2-17.1). The majority received mRNA vaccines. Within RA, 8,727 (7.1%) received &gt;3 doses, 89,583 (72.6%) received 3 doses, 23,652 (19.2%) received 2 doses, and 1,504 (1.2%) a single dose. Within the general population, 373,735 (75.7%) received 3 doses and only 7,963 (1.6%) received &gt;3 doses. Among RA individuals, relative to control periods, event rates were not significantly increased after the first dose in terms of AESIs (RI 1.05 95% CI 0.90-1.22) or ED visits (RI 0.97 95% CI 0.94-1.01). Hospitalizations were slightly lower for RA patient in post-vaccination versus control periods (RI 0.83 95% CI 0.78-0.88). Compared to control periods, rheumatology visits slightly increased after the first dose (RI 1.08 95% CI 1.07-1.10), then decreased after doses 2-3, normalizing after dose 4. Relative to non-RA comparators, RA individuals had a higher relative incidence rate of AESIs after dose 3 (RIR 1.28 95%CI 1.05-1.56) but no differences in hospitalizations or ED visits. Potential limitations of our study include the possibility that individuals avoided additional doses if they had an adverse event after the first dose, and that access to rheumatologists likely changed over time. <h3>Conclusion</h3> In this self-controlled case series, we did not detect a significant increase in AESI or health care use when comparing pre-vaccine to post-vaccine periods in RA. <h3>REFERENCES:</h3> NIL. <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> None Declared.